The present invention relates in general to fluid filters, preferably disposable fluid filters which include a filter cartridge. More specifically the present invention relates to the design and construction of the filter cartridge used in a disposable fluid filter, and focuses on the design of the centertube which is an important component of the fluid filter cartridge. The type of disposable fluid filters discussed herein, in the context of the present invention which incorporate a centertube, are typically used or are associated with diesel engine technology. While the present invention centertube may be used with replaceable filter cartridges, the present invention centertube will be described in the context of a disposable fluid filter.
A review of earlier fluid filter technology reveals that the use of a centertube is quite common, either as a component part of a replaceable filter cartridge or as a component part of a disposable fluid filter. In either arrangement, the centertube is intended to provide support for the filtering element. Fluid filters of the type described herein typically experience a significant differential pressure across the filtering element. This differential pressure in turn provides the possibility of the filter element collapsing into its hollow interior due to this differential pressure. This particular issue has to be addressed in the design of fluid filters, fluid filter cartridges, and centertubes. The preferred design solution is to use the centertube as a support member in order to provide the requisite structural strength to the filter cartridge. Regardless of whether the fluid filter is designed as a disposable unit or configured with a replaceable filter cartridge, there is value in having a properly designed and integrated centertube to provide the needed support to the interior of the filtering element.
Obviously the magnitude of the differential pressure which is seen by the filtering element will have some bearing on the degree of strength and rigidity required of the centertube. If the (fluid) filtering element sees a differential pressure of between 150 psi and 200 psi, conventional centertube designs might still be acceptable. However, higher differential pressures in the 350 psi to 400 psi range require current centertube designs to be reinforced and/or increased in wall thickness or changed as to the materials which are used in order to generate added strength and rigidity. These design changes will cause an increase in the overall cost of the centertube. Accordingly, the importance of the centertube comes into greater focus when the fluid filter is expected to see a relatively high (350-400 psi) differential pressure.
Since a differential pressure in the 400 psi range is not believed to be typical, are there fluid filter design applications where such a differential pressure might be seen? In the context of the present invention, it was desired to design a suitable fluid filter for use with a new high-pressure fuel system. The specifics of the associated components for this new fuel system are influenced by the viscosity of the fuel which may be seen, particularly when cold, and the operation of a gear pump which is used for fuel delivery to the fuel filter. The system analysis which was conducted predicted a need for the filter cartridge to be able to perform with a differential pressure of 380 psi and the system specification was set at 400 psi.
When the filter cartridge needs to be capable of withstanding the pressures created by higher pressure systems, such as the referenced high-pressure fuel system, earlier centertube designs have focused on reinforcement efforts. For example, one design approach simply uses a thick-walled, welded metallic centertube. Another approach uses a somewhat standard metallic lock-seam centertube with an inserted spring support. A still further approach uses a plastic centertube with an inserted plastic post that includes various support ribs. While these early designs may be functional, they tend to be expensive due to the number of components, the material costs, and the labor associated with assembly.
As a result of the need for an improved centertube design from at least a cost perspective, without compromising performance and enabling the centertube to be suitable for the new high-pressure fuel system, the present invention was conceived and reduced to practice. The design of the present invention centertube focuses on a unitary, molded construction with a novel and unobvious cross-beam support which yields a “mold-friendly” centertube design with the requisite strength to handle high differential pressures.